(Not Applicable)
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The present invention relates in general to gas turbines and, more particularly, to swirler assemblies.
Gas turbines generally comprise the following elements: a compressor for compressing air; a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor; and a turbine for expanding the hot gas produced by the combustor.
As shown in FIG. 1, an example of a prior art gas turbine combustor 10 comprises a nozzle housing 12 having a nozzle housing base 14. A diffusion fuel pilot nozzle 16, having a pilot fuel injection port 18, extends through nozzle housing 12 and is attached to nozzle housing base 14. In the shown configuration, main fuel nozzles 20, each having at least one main fuel injection port 22, extend substantially parallel to pilot nozzle 16 through nozzle housing 12 and are attached to nozzle housing base 14. Fuel inlets 24 provide fuel 26 to main fuel nozzles 20. A main combustion zone 28 is formed within a liner 30. A pilot cone 32, having a diverged end 34, projects from the vicinity of pilot fuel injection port 18 of pilot nozzle 16. Diverged end 34 is downstream of main fuel swirlers 36. A pilot flame zone 38 is formed within pilot cone 32 adjacent to main combustion zone 28.
Compressed air 40 from compressor 42 flows between support ribs 44 through main fuel swirlers 36. Each main fuel swirler 36 is substantially parallel to pilot nozzle 16 and adjacent to main combustion zone 28. Within each main fuel swirler 36, a plurality of swirler vanes 46 generate air turbulence upstream of main fuel injection ports 22 to mix compressed air 40 with fuel 26 to form a fuel/air mixture 48. Fuel/air mixture 48 is carried into main combustion zone 28 where it combusts. Compressed air 50 enters pilot flame zone 38 through a set of stationary turning vanes 52 located inside pilot swirler 54. Compressed air 50 mixes with pilot fuel 56 within pilot cone 32 and is carried into pilot flame zone 38 where it combusts.
FIG. 2 shows a detailed view of an exemplary prior art fuel swirler 36. As shown in FIG. 2, fuel swirler 36 is substantially cylindrical in shape, having a flared inlet end 58 and a tapered outlet end 60. A plurality of swirler vanes 46 are disposed circumferentially around the inner perimeter 62 of fuel swirler 36 proximate flared end 58. In the shown configuration, fuel swirler 36 surrounds main fuel nozzle 20 proximate main fuel injection ports 22. Fuel swirler 36 is positioned with swirler vanes 46 upstream of main fuel injection ports 22 and tapered end 60 adjacent to main combustion zone 28. Flared inlet end 58 is adapted to receive compressed air 40 and channel it into fuel swirler 36. Tapered outlet end 60 is adapted to fit into sleeve 64. Swirler vanes 46 are attached to a hub 66. Hub 66 surrounds main fuel nozzle 20.
FIG. 3 shows an upstream view of combustor 10. Pilot nozzle 16 is surrounded by pilot swirler 54. Pilot swirler 54 has a plurality of stationary turning vanes 52. Pilot nozzle 16 is surrounded by a plurality of main fuel nozzles 20. A main fuel swirler 36 surrounds each main fuel nozzle 20. Each main fuel swirler 36 has a plurality of swirler vanes 46. The diverged end 34 of pilot cone 32 forms an annulus 68 with liner 30. Main fuel swirlers 36 are upstream of diverged end 34. Fuel/air mixture 48 flows through annulus 68 (out of the page) into main combustion zone 28 (not shown in FIG. 3).
Fuel swirler 36 is attached to liner 30 via attachments 70 and swirler base 72. With respect to the latter manner of attachment, the distal end of sleeve 74 is adjacent to the swirler base plate 72 as shown in FIG. 2. The distal end of sleeve 74 and the base plate 72 typically do not come into contact and are actually spaced approximately 10 mils apart. FIG. 3 shows a circular array of six swirlers, but other quantities, such as a series of eight swirlers, can be employed.
The other manner of attaching the swirler 36 to liner 30 is by way of attachments 70. In initial designs, attachments 70 comprised dual straight pins, each pin being welded at one end to liner 30 and at the other end to the swirler 36. This design, however, often fails due to fatigue induced cracking of the pins at the support casing. One prior design revision includes replacing the straight pin attachments with hourglass-shaped pins (as shown) to provide improved weld areas on both the swirler 36 and the liner 30. However, this design also suffers from fatigue-related failures, primarily occurring at the weld joint between the hourglass-shaped pin attachments 70 and the swirler 36.
The fatigue failures stem from a swirler""s exposure to vibrational forces generated during combustor operation. Combustion dynamics typically range from approximately 110-150 Hz, although variations outside this range are possible depending on the system design. Prior swirlers, when only adjacent to or abutting the base plate, generally had a natural frequency of approximately 145 Hz, falling within the typical vibrational range experienced during combustion dynamics. Consequently, when a swirler is subjected to such forces, the swirler will resonate, and repeated resonance of the swirler ultimately fatigues the weld joints of the support pins.
Thus, high cycle fatigue failures are a recurring problem with respect to swirlers and other turbo machinery components. The problem has been exacerbated by combustion design changes to reduce emissions and increase efficiency. These design changes have increased the severity of the combustion dynamics, requiring more robust swirler assemblies. Therefore, there is a continuing need for a swirler assembly that can avoid vibration-induced resonance and that can further enhance the inherent damping characteristics of the swirler to constrain any vibratory motion.
It is an object of the invention to provide a swirler assembly that is adapted to tolerate the severity of the dynamics of combustors designed for reduced emissions and greater efficiencies.
It is another object of the invention to provide a more robust swirler assembly that can accommodate changes due to thermal expansion.
These and other objects of the invention are achieved by a swirler assembly adapted to interface with a supporting base plate so as to raise the resonant frequency of the swirler assembly above the vibrational range of the combustion environment and to increase the damping of the swirler response to the combustion dynamics. The present invention applies particularly to a swirler assembly that includes a swirler, a generally cylindrical swirler sleeve and a plate. The swirler has an inlet and an outlet end. The sleeve has a proximal end and a distal end. The outlet end of the swirler extends into the sleeve through the proximal end. The plate has an opening that, due to manufacturing processes, is elongated into an elliptical shape.
According one aspect of the invention, the distal end of the sleeve extends into the plate opening and contacts the inner ring-like surface of the plate opening at least partially around its periphery so that portions of the sleeve contact the surface along the minor axis of the elliptical opening and transition to a clearance along the major axis. The contact areas between the sleeve and the plate stiffen the interface and increase the natural frequency of the swirler. For example, the natural frequency can be increased to 700 Hz, well above the operational combustion dynamics, in the neighborhood of 110-150 Hz. The contact areas also increase frictional forces to damp the vibrational response of the swirler.
The sleeve preferably tapers from a larger diameter outside the plate opening down to the diameter of the portion that extends into, and preferably through, the opening. The shape of the taper preferably substantially follows the profile of the plate into the opening. The matching profile increases the areas of contact between the sleeve and the plate, increasing the stiffness and the surface area for generating frictional damping forces.
The clearance in the region of the major axis of the elliptical plate opening accommodates thermal stresses that can arise from expansion of the sleeve in the high temperature environment of the combustor. Thus, the swirler assembly according to aspects of the invention avoids resonance and damps vibrational responses while providing for thermal expansion.
In another aspect, a turbo machinery assembly includes a turbo machinery component and a plate having an opening. The opening defines an inner surface. The turbo machinery component has a first end and a second end. The second end of the turbo machinery component has an outer profile that substantially follows the inner surface and substantially adjacent to at least a portion of the plate surrounding the opening. The outer profile contacts a portion of the inner surface while providing clearance in other regions along the opening periphery. The turbo machinery assembly has a natural frequency outside of the range of operational vibrational forces and further has increased damping capability.
In still another aspect, the present invention is directed to a method for altering the natural frequency and enhancing the damping characteristics of a swirler. The method includes the steps of: providing a plate having an opening, which defines an inner surface; providing a swirler having an inlet end and an outlet end; providing a sleeve having a first end and a second end, the second end having an outer surface substantially conforming to the inner annular surface and to a portion of the plate surrounding the opening; placing the outlet end of the swirler into a first end of a sleeve; and placing the second end of the sleeve into the opening such that the second end of the sleeve substantially contacts a portion of the inner surface of the opening and adjacent to the opening while providing clearance in other regions of the opening periphery.
In a further aspect of the invention, the stabilization provided by the sleeve engagement with the base plate can permit the use of a single pin for supporting the swirler from the surrounding shell. The single pin can be cast, providing further manufacturing savings.
Thus, the invention provides a swirler assembly that can more readily endure combustion dynamics and high temperature conditions while presenting opportunities for manufacturing economies.